Backpack



FIG. 1 is a left perspective view of a backpack showing my new design;

FIG. 2 is a front view thereof; and,

FIG. 3 is a right perspective view thereof.

The uneven-length broken lines represent unclaimed boundaries of the design. The unshaded region within the shaded area that is demarcated by uneven-length broken lines forms no part of the claimed design. The even-length broken lines showing the remainder of the backpack are for environmental purposes only and form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 